Resistor alloy



United States Patent RESISTOR ALLOY John Harry Jackson, Columbus, Ohio,and James F.

Kavanaugh, Westport, Conn., assignors, by mesne assignments, to The C.O. Jelliff Manufacturing Corporation, Southport, (301211., a corporationof Connecticut No Drawing. Application October 31, 1956, Serial No.619,401

5 Claims. (Cl. 75--171) This invention relates to resistor alloys and isparticularly directed to the provision of an improved alloy forfabrication into wires for wire-wound electrical resistance elements.The invention provides an improved alloy amenable to production andfabrication on a commercial scale and by commercially practicalprocedures, which can consistently be formed into Wires and otherarticles having a high electrical resistivity and a very low (andgenerally positive) temperature coefiicient of resistivity.

The alloy of this invention consists essentially of 8% to 28% chromium(all percentage composition figures herein are by weight), to 36%manganese, 0.1% to 4% molybdenum, 0.1% to 3% aluminum, /z% to 5% cobalt,and the balance nickel. Such an alloy, in the annealed condition,possesses an electrical resistivity of approximately 800 ohms percircular mil foot and has a temperature coefiicient of resistivityWithin the range +0.00001 to 0.00001 ohm per ohm per C.

Preferably, electrical resistance alloys according to the invention fallwithin the somewhat narrower composition range of 15% to 25 chromium,15% to 25% manganese, 1% to 3% molybdenum, 0.1% to 1.0% aluminum, /z% to5% cobalt, and the balance nickel, the nickel preferably constitutingfrom 50% to 70% of the alloy. The resistivity of these alloys isgenerally near or above 800 ohms per circular mil foot, while thetemperature coefficient of resistivity is at a value between +0.00001and 0.0000l. A particularly advantageous alloy according to theinvention is one consisting essen' tially of about chromium, about 18%manganese, about 1.5% molybdenum, about 0.25% aluminum, about 1.5%cobalt, and the balance nickel.

Alloys composed essentially of chromium, manganese and molybdenum withinthe ranges stated above, and the balance nickel, have been produced andused heretofore as electrical resistance alloys. Indeed, such alloys canbe heat treated (solution annealed and then aged) to develop very highelectrical resistivity, in the neighborhood of 1000 ohms per circularmil foot. However, it is very difficult under commercial manufacturingconditions to produce wires of such alloys which consistently possesselectrical resistivities above about 750 ohms per circular rnil foot.Moreover, it is difficult to avoid embrittlement of wires of such alloysin their manufacture when they are heat treated (solution annealed andthen aged) to possess high electrical resistivity (i. e. above about 750ohms per circular mil foot). In addition, wires fabricated commerciallyof such alloys generally possess a temperature coefficient ofresistivity substantially exceeding 10 parts per million.

The present invention is based on the discovery that by adding aluminumand cobalt in the ranges stated above to the base alloy of chromium,manganese, nickel and molybdenum in the amounts stated above, a notableimprovement in the electrical resistivity and a notable narrowing of therange of the temperature coefiicient of resistivity of the alloy issecured. The aluminum addition favorably influences the resistivity,while additions of co- 2,817,586 Patented Dec. 24, 1957 balt have beenfound to constitute an eifective means of controlling the temperaturecoefiicient of resistivity of "the alloy. Such alloys, containingaluminum and cobalt, can be readily and consistently produced andfabricated into wires by conventional commercial techniques, which wiresconsistently possess, as annealed, electrical resistivities of about 800ohms per circular mil foot. Furthermore, the aluminumand cobalt-bearingalloys of this in vention have a very small temperature coefiicient ofresistivity, less than 10 parts per million, and generally of positivesign (i. e., resistivity increases slightly with increase intemperature).

Optimum properties are developed in alloys of this invention byannealing the metal at a temperature in the range from 1500 F. to 2100F., and preferably in the upper portion of this range, that is, from1700 F. to 2100 F. The time required for the annealing treatment dependson the annealing temperature, ranging from as much as 100 hours at atemperature of 1500 F. to as little as two seconds (in the case of finewires) at a temperature of 2100 F. The time required for annealing is ofcourse also dependent on the physical size of the article being treated,being much less for small diameter wires than for large diameter bars orrods. It is also to some extent dependent on the prior history of thealloy. For example, if the alloy is in the as-cast condition, theannealing time must be longer than if the alloy has undergone somemeasure of mechanical working. In the annealed condition, the metal isreadily worked by conventional cold rolling and cold drawing operationsto produce strips and wires that are subsequently to be fabricated intoelectrical resistance devices.

Following is an example of this invention: An alloy composed essentiallyof 19.5% chromium, 18.5% manganese, 1.5 molybdenum, 1.0% aluminum, 3,0%cobalt, and the balance nickel was melted and cast, forged into smallbars about /2 inch square in cross section, swaged to %-1I1Ch diameterrod, and then cold drawn into the form of round wire about 0.01 inch indiameter. The wire was annealed by heating it at 1800" F. for approximately /2 hour, and then was air cooled to room temperature. Theresulting wire had an electrical resistivity of 789 ohms per circularmil foot, and a temperature coetficient of resistivity of +0.000004.This wire was readily formed into resistor coils and other shapes.

In preparing the alloys of this invention, it is the usual practice toadd silicon in amounts of about 0.2% as a deoxidizer. This addition,together with silicon from the original charge, often results in aresidual silicon content of from 0.35% to 0.4%, without affecting theproperties of the alloy. In a similar way, titanium in amounts up toabout 0.2% is often added to effect grain refinement. The presence orabsence of such elements is immaterial to the alloys of this invention.

Other examples of alloys according to this invention are set forth inthe following table:

Com osition p Resistivity '1. 0., p. p. 111. Cr Mn 00 Mo Al 1Oomposition-balance nickel plus impurities, deoxidizer, and grainResistivity-411 ohms per circular mil foot. y 1 Temperature eoeflieientof resistivity-in parts per million.

We claim: 1. An electrical resistance alloy consisting essentially of 8%to 28% chromium, 15% to 36% manganese, 0.1%

. 3 to 4% molybdenum, 0.1% to 3% aluminum, /2% to 5% cobalt, and thebalance nickel.

2. An electrical resistance alloy consisting essentially of to 25%chromium, 15% to 25% manganese, 1% t0 3% molybdenum, 0.1% to 1.0%aluminum, /z% to 5% cobalt, and the balance nickel, said nickelconstituting 50% to 70% of the alloy.

3. An electrical resistance alloy consisting essentially of aboutchromium, about 18% manganese, about 1.5% molybdenum, about 0.25%aluminum, about 1.5% cobalt, and the balance nickel.

4. An electrical resistance alloy consisting essentially of 8% to 28%chromium, 15% to 36% manganese, 0.1% to 4% molybdenum,0.1% to 3%aluminum, /2% to 5% cobalt, and the balance nickel, said alloy being inthe annealed condition and having an electrical resistivity ofapproximately 800 ohms per circular mil foot and having a temperaturecoefiicient of resistivity within the range from +0.00001 to -0.0000l.

S. An electrical resistance alloy consisting essentially of 15% tochromium, 15% to 25% manganese, 1% to 3% molybdenum, 0.1% to 1%aluminum, 42% to 5% cobalt, and the balance nickel, said nickelconstituting to of the alloy, and said alloy being in the annealedcondition and having an electrical resistivity of approximately 800 ohmsper circular mil foot and having a temperature coefiicient ofresistivity from +0.0000l to 0.00001.

No references cited.

1. AN ELECTRICAL RESISTANCE ALLOY CONSISTING ESSENTIALLY OF 8% TO 2,%CHROMIUM, 15% TO 36% MANGANESE, 0.1% TO 4% MOLYBEDENUM,0.1% TO 3%ALUMINUM, 1/2% TO 5% COBALT, AND THE BALANCE NICKEL.